The value of compost

What You Will Need:

• Well-rotted compost (if necessary sieve to remove lumps).
• Trowels and gloves.
• Pen and paper.
• Poor quality garden soil that has not been fertilised or had compost added for a long time.
• Two identical plastic cups with holes in the bottom, or two identical plant pots.
• A label for each pot.
• Two identical seedling vegetables from the same batch, e.g. from a punnet of lettuce seedlings.
• A measuring jug.

What to do

1. Plant one of the seedlings in a plastic cup or plant pot using garden soil only.
2. Plant the other seedling in a mix of 50% compost and 50% garden soil. The garden soil needs to be from the same place as above and the compost and garden soil need to be well mixed.
   
   
   
3. Label each pot.
4. Water them well using exactly the same amount of water, check daily and continue to keep them damp by again using exactly the same amount of water for each pot every time.
5. Place both pots alongside each other where they receive equal amounts of sunlight.
6. Every week record for each plant: the number of leaves, its longest leaf, and any other findings about its growth, e.g. colour of leaves and their thickness. Take a picture of them both alongside each other. What you record will depend on the type of seedlings you choose to grow.

Questions

1. State at least three ways you made this experiment a 'fair test'.
2. Which plant grew better? State your evidence for this.
3. Did the compost help the plant grow better? Explain why or why not the compost might have affected the growth.

Related resources

The need for nutrients

Photo credit: Good compost (Peter E. Smith, NSIL).